File 5e7dfbf6-x86-ucode-AMD-potential-buffer-overrun-equiv-tab.patch of Package xen.14764

# Commit 1f97b6b9f1b5978659c5735954c37c130e7bb151
# Date 2020-03-27 13:13:26 +0000
# Author Andrew Cooper <andrew.cooper3@citrix.com>
# Committer Andrew Cooper <andrew.cooper3@citrix.com>
x86/ucode/amd: Fix potential buffer overrun with equiv table handling

find_equiv_cpu_id() loops until it finds a 0 installed_cpu entry.  Well formed
AMD microcode containers have this property.

Extend the checking in install_equiv_cpu_table() to reject tables which don't
have a sentinal at the end.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/microcode_amd.c
+++ b/xen/arch/x86/microcode_amd.c
@@ -297,6 +297,7 @@ static int install_equiv_cpu_table(
     size_t *offset)
 {
     const struct mpbhdr *mpbuf = data + *offset + 4;
+    const struct equiv_cpu_entry *eq;
 
     *offset += mpbuf->len + CONT_HDR_SIZE;	/* add header length */
 
@@ -306,7 +307,9 @@ static int install_equiv_cpu_table(
         return -EINVAL;
     }
 
-    if ( mpbuf->len == 0 )
+    if ( mpbuf->len == 0 || mpbuf->len % sizeof(*eq) ||
+         (eq = (const void *)mpbuf->data,
+          eq[(mpbuf->len / sizeof(*eq)) - 1].installed_cpu) )
     {
         printk(KERN_ERR "microcode: Wrong microcode equivalent cpu table length\n");
         return -EINVAL;